Experimental Infections in Cattle and Sheep with Haemonchus contortus Resistant or Susceptible to Benzimidazole Treatments

Abstract

In order to evaluate the potential risk of Haemonchus contortus resistant to benzimidazole (BZ) treatments to pass from sheep to cattle a series of experiments were carried out. Two field isolates of H. contortus resistant (Ayacucho) or susceptible (Cedive) to BZ treatments were reproduced in lambs and involved in the study. Two groups of 4 calves each and two groups of 4 lambs each were infected with larvae (L3) of each isolate respectively. The number of eggs in faeces (EPG), worm count and ratio of worm establishment (RWE) were determined. The number of red blood cells, packed cell volume and haemoglobin concentration was assessed. The EPG levels were higher for Ayacucho isolate which reached to a peak of 7,168 and 780 at day 42 post inoculation (PI) in lambs and calves respectively. The RWE at day 45 PI was 28.8 % and 7.16% for Ayacucho isolate in lambs and calves respectively while for Cedive isolate was 36.6% and 0.04% respectively. At day 90 PI the RWE was of 1.94% and 0.69% in lambs for Ayacucho and Cedive isolate respectively, whereas no worms were recovered from calves. The haematological parameters in lambs and calves did not show significant differences between isolates. The present studies demonstrate that some populations of H. contortus may complete life cycle in calves and remain established for at least a 45 days period PI. This finding should be strongly considered when farm production involves mixed or alternate sheep/cattle grazing and backgrounds of anthelmintic resistance.